Iron-based phyllosilicate material for efficiently removing variable-valence heavy metals and water treatment application of iron-based phyllosilicate material

Abstract

The invention discloses an iron-based layered silicate material for efficiently removing variable-valence heavy metals and water treatment application of the iron-based layered silicate material, and belongs to the technical field of water treatment.The preparation method of iron-containing layered silicate minerals comprises the following steps that ferrous sulfate heptahydrate is dissolved in water, sodium dithionite and sodium orthosilicate are sequentially added, stirring is conducted, and a mixture is obtained; stirring, homogenizing and aging for two hours; the hydrothermal reaction kettle is used for reacting in a high-temperature and high-pressure environment; according to the iron-containing layered silicate mineral material, a unique layered structure similar to natural iron-containing layered silicate minerals and high adsorption performance are reserved, variable-valence heavy metal arsenic in a wastewater solution is synergistically and efficiently removed by means of the oxidation-reduction activity of the iron-containing layered silicate mineral material and induction of generation of Fenton-like reaction, and the iron-containing layered silicate mineral material is obtained. The method disclosed by the invention shows high treatment efficiency, environmental friendliness and remarkable economic benefits, and is expected to exert remarkable environmental benefits in the field of water treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to an iron-based silicate material for efficiently removing variable-valence heavy metals and its water treatment application. Background Art

[0002] The pollution problem of variable-valence heavy metal arsenic has attracted increasing attention worldwide, mainly due to the fact that these metal elements can exist in multiple valence states, easily accumulate in soil and water bodies, and have a wide range of impacts on the environment and the health of organisms. According to global reports, about 200 million people face health risks from consuming arsenic-contaminated drinking water. In addition, variable-valence heavy metal arsenic has different chemical behaviors in the environment, and its toxicity and bioavailability change with the valence state. Trivalent arsenic (As(III)) is more toxic and mobile than pentavalent arsenic (As(V)), and the difference in heavy metal valence states makes the control and remediation of heavy metal pollution more complicated. Therefore, there is an urgent need to develop new technologies to meet these challenges.

[0003] Numerous studies have shown that layered silicate minerals have been widely studied and applied in the treatment of heavy metal pollution, mainly due to their unique structural characteristics. Layered silicate minerals are mainly divided into 2:1 type (such as montmorillonite and illite) and 1:1 type (such as kaolinite). They have a large specific surface area, abundant surface active sites and high ion exchange capacity, which enable them to effectively adsorb and fix heavy metal ions. In addition, most layered silicate minerals contain iron (Fe), ranging from trace amounts to 30% wt, of which 90% is structural iron, present in tetrahedrons and octahedrons. The structural iron in the octahedral position exists in a valence state of +2 or +3, and the mutual conversion between the two valence states can be observed under redox conditions and changes in microbial activity. Studies have shown that iron-containing layered silicate minerals have high heterogeneous catalytic potential, such as redox reactions and Fenton-like reactions, in which the principle of redox reactions is to use the electron transfer process between Fe (II) / Fe (III) in iron-containing layered silicate minerals to achieve oxidation and reduction reactions. For example, Ilgen A et al. reported in a paper published in Environmental Science and Technology, Vol. 51, pp. 11105-11114 in 2017 that natural iron-containing silicate minerals (nontronite (NAu-1)) can oxidize arsenic (III) to arsenic (V) under aerobic and anoxic conditions; Wu et al. reported in a paper published in Water Research, Vol. 267, pp. 122548 in 2024 that Fe (II) in iron-containing layered silicate minerals can promote the reduction of Cr (VI) to Cr (III). The principle of the Fenton-like reaction is to use the reaction of Fe (II) in iron-containing layered silicate minerals with hydrogen peroxide to produce hydroxyl radicals with strong oxidizing ability. The specific reaction process can be expressed as: Fe 2++ H 2 O 2 → Fe 3+ +OH + OH - The generated reactive oxygen species can effectively remove variable heavy metals and reduce their toxic effects on the ecosystem. Therefore, iron-containing layered silicate minerals have good application prospects in removing variable heavy metals.

[0004] However, past studies have found that most of the Fe in natural iron-containing silicate minerals exists in the form of Fe (III), and a reduction process is required to introduce sulfur / organic reducing agents or reducing microorganisms to promote the conversion of Fe (III) in clay minerals into Fe (II) to have redox activity. For example, the reducible and activated iron-containing silicate minerals reported in patent CN111908585A are prepared using reducing organic polyphenols; patent CN107381770B uses chemical reduction (hydrogen peroxide, sodium bicarbonate-sodium citrate mixture) to prepare active iron-containing silicate minerals. At the same time, the activation of Fe (II) in natural iron-containing silicate minerals is not very active and is easily oxidized and inactivated (the removal rate of arsenic is only 74%, and the inactivation of natural minerals in 1h is >50%), and a reducing agent needs to be added cyclically. Therefore, this not only has a complex reduction process, but is also prone to high costs and secondary environmental pollution. For bioengineering, the maintenance cost is high and the treatment cycle is long. Secondly, in nature, the formation of iron-containing phyllosilicate minerals is related to the Fe / Si ratio. Different Fe / Si ratios can lead to different mineral structures, properties and activities. However, due to geological conditions, it is difficult to achieve precise control of the Fe / Si ratio. At the same time, natural iron-containing silicate minerals are impure in structure due to environmental influences, and their activity is easily affected by impurities.

[0005] Therefore, in order to solve the above problems, this technology uses a hydrothermal synthesis method to precisely control the Fe / Si molar ratio to 0.5–2.0 (preferably 0.75–1.5), construct a lattice structure with a high proportion (>85%) of octahedral Fe(II / III), and achieve a directional improvement in the redox ability of the mineral. The synthesized iron-containing layered silicate mineral has a pure structure, and the one-step preparation does not require post-reduction, saving more than 30% of the cost. The lattice-locked Fe(II / III) maintains an activity of >85% for a long time under pH 3–9 and dissolved oxygen conditions; the adsorbent itself oxidizes As(III)+ to catalyze H 2 O 2 Oxidize As(V) to achieve simultaneous removal of all valence arsenic (total arsenic removal efficiency >99%). Summary of the invention

[0006] The purpose of the present invention is to propose an iron-based layered silicate material for efficiently removing variable-valence heavy metals and its water treatment application, prepare an iron-containing layered silicate mineral with adjustable Fe / Si by hydrothermal synthesis, and use the high activity of its structural Fe to achieve simultaneous redox reaction and Fenton reaction to treat arsenic-containing wastewater. The present invention provides a new way to remove variable-valence heavy metal arsenic, and also solves the problems of high material cost, easy to cause secondary pollution and complex process in the prior art.

[0007] In the first aspect, the present application proposes an iron-based silicate material for efficiently removing variable-valence heavy metals, which is prepared from the following raw materials, wherein the raw materials include ferrous sulfate 7hydrate, sodium orthosilicate and sodium dithionite; wherein ferrous sulfate 7hydrate and sodium orthosilicate are used as iron sources and silicon sources, sodium dithionite is used as a reducing agent, the molar ratio of ferrous sulfate 7hydrate and sodium orthosilicate is 1:1-3:2, and the mass percentage of iron in the silicate mineral material is not less than 10%.

[0008] Furthermore, the Fe / Si molar ratio of the iron-containing layered silicate mineral material is 0.75-2, preferably 1.0-1.5.

[0009] Furthermore, the iron-containing layered silicate mineral material has a lattice structure with a high proportion of octahedral Fe(II / III).

[0010] Furthermore, the iron-containing layered silicate mineral material does not require post-reduction.

[0011] In a second aspect, the present invention also provides a method for preparing an iron-based silicate material for efficiently removing variable-valence heavy metals, comprising the following steps: S1: dissolving ferrous sulfate heptahydrate in deionized water, adding sodium dithionite and sodium orthosilicate under stirring, and continuously stirring to obtain a mixed suspension; S2: subjecting the mixed suspension obtained in step S1 to a hydrothermal reaction to obtain a reaction composition; S3: washing, centrifuging and freeze-drying the reaction product obtained in step S2 to obtain an iron-containing layered silicate mineral.

[0012] Furthermore, the stirring time in S1 is 1-4 hours.

[0013] Furthermore, the molar ratio of the ferrous sulfate heptahydrate to sodium orthosilicate is 1:1-3:2.

[0014] Further, the Fe / Si molar ratio is 0.75–2.0.

[0015] Furthermore, the hydrothermal reaction temperature in step S2 is 130-160° C., and the hydrothermal reaction time is 4-10 days, preferably 6-8 days.

[0016] In a third aspect, the present invention also provides an application of the iron-based silicate material for efficiently removing variable-valence heavy metals in water treatment, comprising the following steps: S1: dispersing the iron-containing layered silicate mineral material in deionized water to prepare an iron-containing layered silicate mineral suspension, and adjusting the pH value of the suspension with a buffer solution; S2: using a buffer to adjust the pH value of the variable valence heavy metal solution to be the same as the pH value of the iron-containing layered silicate mineral suspension in S1; S3: Mixing the variable valence heavy metal solution and the iron-containing layered silicate mineral suspension.

[0017] Furthermore, the buffers in S1 and S2 are MES and MOPS.

[0018] Furthermore, the heavy metal is arsenic.

[0019] Furthermore, the removal rate of the variable-valence heavy metals is determined by liquid chromatography-atomic fluorescence spectrometry, which can separate different forms of compounds of the same metal in the sample and detect the content of various forms of compounds using atomic fluorescence technology.

[0020] The beneficial effects of this application include: 1. The iron-containing phyllosilicate mineral prepared by the present invention has properties similar to those of natural iron-containing phyllosilicate minerals, has a layered structure, a large specific surface area, abundant surface active sites and a high ion exchange capacity, and can effectively adsorb and fix variable valence heavy metals.

[0021] 2. The activity of the structural Fe of the synthesized iron-containing layered silicate minerals is fully utilized. The structural Fe (Ⅱ / Ⅲ) is used to activate oxygen under neutral conditions to produce hydroxyl radicals and its own redox activity, and the variable valence heavy metals in water and adsorbed on the surface of the iron-containing layered silicate minerals are synergistically removed. It has the characteristics of high removal efficiency and environmental friendliness.

[0022] 3. The prepared iron-containing layered silicate mineral synthetic material is low-priced and easy to obtain. The iron in the iron-containing layered silicate mineral is rarely released into the aqueous solution during the reaction with the variable-valence heavy metal, thereby effectively preventing the loss of iron elements and the generation of iron mud. The treated material can also be recycled and reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Physical characteristics of the iron-containing phyllosilicate minerals prepared in Examples 1 and 2.

[0024] Figure 2X-ray diffraction patterns of the iron-containing layered silicate minerals prepared in Example 1 and Example 2.

[0025] Figure 3 This is the Fourier transform infrared analysis spectrum of the iron-containing layered silicate minerals prepared in Example 1 and Example 2.

[0026] Figure 4 This is a scanning electron microscope image of the iron-containing layered silicate minerals prepared in Example 1 and Example 2.

[0027] Figure 5 This is a diagram showing the removal effect of variable-valence heavy metal arsenic by the prepared iron-containing layered silicate mineral under neutral conditions.

[0028] Figure 6 This is a diagram showing the removal effect of variable-valence heavy metal arsenic by iron-containing layered silicate minerals under different pH conditions.

[0029] Figure 7 For PO 4 3- Figure 3 is a diagram showing the removal effect of the variable-valence heavy metal arsenic by the iron-containing layered silicate mineral prepared in Example 1 under the following conditions.

[0030] Figure 8 This is a graph showing the stability test results of the iron-containing layered silicate mineral prepared in Example 1 to variable-valence heavy metal arsenic.

[0031] Fig. 9 The economic benefits of removing arsenic from the iron-containing layered silicate minerals and other minerals prepared in Examples 1 and 2. DETAILED DESCRIPTION

[0032] The present application is described in detail below in conjunction with the examples, but the present application is not limited to these examples. The raw materials in the examples of the present application can all be purchased through commercial channels.

[0033] The raw materials used in the embodiment are as follows: Ferrous sulfate 7hydrate: analytical grade, purchased from MacLean Company.

[0034] Sodium orthosilicate: analytical grade, purchased from Maclean Company.

[0035] Sodium dithionite: analytical grade, purchased from Maclean Company.

[0036] Sodium arsenite: analytical grade, purchased from Aladdin Company.

[0037] MES buffer: analytical grade, purchased from MacLean.

[0038] MOPS buffer: analytical grade, purchased from MacLean. Example 1

[0039] This embodiment provides an iron-containing layered silicate material for efficiently removing variable-valence heavy metals. The preparation method of the iron-containing layered silicate mineral material comprises the following steps: S1. Preparation of iron-containing layered silicate minerals (Fe / Si=1.0).

[0040] S11. Add 3.541 g of ferrous sulfate heptahydrate (0.0127 mol) into a conical flask and dissolve it in 70 ml of deionized water. Then, quickly add 0.044 g of sodium dithionite while stirring, and then add 2.356 g of sodium orthosilicate (0.0128 mol), and continue to stir evenly for 2 hours.

[0041] S12, pour the above mixed solution into a hydrothermal reactor with a specification of 100 ml, heat to 150° C., and react for 6 days.

[0042] S13. The reaction product was collected using a centrifuge at a speed of 10000 r / min, then washed with deionized water three times, and finally placed in a vacuum freeze dryer for 24 hours to obtain an iron-containing layered silicate mineral. Example 2

[0043] This embodiment provides an iron-containing layered silicate material for efficiently removing variable-valence heavy metals. The preparation method of the iron-containing layered silicate mineral material comprises the following steps: S1. Preparation of iron-containing layered silicate (Fe / Si=1.5).

[0044] S11 Add 4.530g of ferrous sulfate heptahydrate (0.0163mol) into a conical flask, dissolve it with 70ml of deionized water, then quickly add 0.042g of sodium dithionite while stirring, and then add 1.997g of sodium orthosilicate (0.0108mol), and stir evenly for 2 hours.

[0045] S12, pour the above mixed solution into a hydrothermal reactor with a specification of 150mL, heat to 150°C, and react for 6 days.

[0046] S13. The reaction product was collected by centrifuge at 10000 r / min, washed with deionized water for 3 times, and dried in a vacuum freeze dryer for 24 h to obtain an iron-containing layered silicate mineral. Example 3

[0047] Evaluation of the removal effect of variable-valence heavy metal arsenic.

[0048] Experimental protocol: 1. Weigh 1g of iron-containing layered silicate mineral powder and add it to 100ml of deionized water (10g / L). Use MES and MOPS buffers to adjust the pH of the suspension to 6, 7 and 8; 2. Weigh 0.0347 g of sodium arsenite and dissolve it in 1 L of water (20 mg / L arsenic). Use MES and MOPS buffer to adjust the pH to the same as the pH of the iron-containing layered silicate mineral suspension. 3. Take 2.5 mL of the above-prepared iron-containing layered silicate mineral suspension and the variable valence heavy metal solution, mix them, and perform an oxygen exposure reaction for 30 min before adsorption oxidation, and then place them on a shaker (rotation speed is 120 rpm) for adsorption oxidation reaction; 4. After a certain reaction time, use a 5mL syringe and a 0.22 uM filter membrane to collect the supernatant, and then use liquid chromatography-atomic fluorescence spectrometry to determine the concentration of heavy metal arsenic. Example 4

[0049] The interfering ion PO 4 3- Evaluation of the removal effect of variable-valence heavy metal arsenic in the presence of.

[0050] Experimental protocol: 1. Weigh 1g of iron-containing layered silicate mineral powder (Fe / Si=1.0) and add it to 100ml of deionized water (10g / L). Use MES and MOPS buffer to adjust the pH of the suspension to 7; 2. Weigh 0.0694 g of sodium arsenite and dissolve it in 1 L of water (40 mg / L arsenic). Use MES and MOPS buffer to adjust the pH to the same pH as the iron-containing layered silicate mineral suspension. 3. Weigh 0.1819 g of sodium dihydrogen phosphate and dissolve it in 1 L of water (40 mg / L phosphorus). Use MES and MOPS buffer to adjust the pH to the same pH as the iron-containing layered silicate mineral suspension. 4. Take 2.5 ml of the above-prepared iron-containing layered silicate mineral suspension and 1.25 ml of the variable valence heavy metal solution and sodium dihydrogen phosphate solution, mix them, and perform an oxygen exposure reaction for 30 minutes before adsorption oxidation, and then place them on a shaker (rotation speed is 120 rpm) for adsorption oxidation reaction; 5. After a certain reaction time, use a 5mL syringe and a 0.22 uM filter membrane to collect the supernatant, and then use liquid chromatography-atomic fluorescence spectrometry to determine the concentration of heavy metal arsenic. Example 5

[0051] TCLP (Toxicity Characteristic Leaching Procedure) test of iron-bearing phyllosilicate minerals (Fe / Si=1.0).

[0052] Experimental protocol: 1. Weigh 2 g of iron-containing layered silicate mineral powder (Fe / Si=1.0) and add it to 200 ml of deionized water (10 g / L). Use MES and MOPS buffer to adjust the pH of the suspension to 7. 2. Add 200 ml of 20 mg / L sodium arsenite solution to the iron-containing layered silicate mineral suspension, use MES and MOPS buffer to adjust the pH to the same pH as the iron-containing layered silicate mineral suspension, react for 24 hours, centrifuge and filter, and place the remaining solid in a vacuum freeze dryer for 24 hours; 3. 5.7 ml of glacial acetic acid was added to 500 ml of deionized water and 64.3 1 mol / L sodium hydroxide solution to obtain extract #1. This step was repeated, and after the preparation, 0.57 g of ascorbic acid was added to obtain extract #2. The role of ascorbic acid is to prevent the leached trivalent arsenic from being reduced. 4. Weigh two portions of 0.5g of iron-containing layered silicate mineral (Fe / Si=1.0) after 24h reaction, add 10ml of leaching solution #1 and 10ml of leaching solution #2 respectively at a liquid-to-solid ratio of 20:1, and place the mixture in a rotary mixer at a speed of 30 rpm for 18 hours; 5. The supernatant was collected using a 5 mL syringe and a 0.22 uM filter membrane, and then the concentration of heavy metal arsenic was determined using a liquid chromatography-atomic fluorescence spectrometer.

[0053] Specifically, the specific surface area and cation exchange capacity in the sample were measured using a fully automatic specific surface area and porosity analyzer (BET) and hexaamminecobalt trichloride ultraviolet spectrophotometry. The iron-containing layered silicate minerals were qualitatively analyzed using natural oriented sheet treatment, ethylene glycol saturation and high-temperature calcination, wherein the natural oriented sheet treatment is to dissolve a small amount of sample in water, and then use a rubber-tipped dropper to draw the dispersion into the oriented sheet for natural drying; ethylene glycol saturation is to place the natural oriented sheet in a drying dish filled with ethylene glycol and heat it at 65°C for steam saturation for 24 hours; high-temperature calcination is to place the natural oriented sheet in a muffle furnace and heat it to 550°C for calcination for 2 hours. The above treatments were analyzed using an X-ray diffractometer. In addition, Fourier transform infrared spectrometers and scanning electron microscopes were used to perform additional characterization analyses on the iron-containing layered silicate minerals in implementations 1 and 2. The analysis results are as follows Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, at the same time, the iron-containing layered silicate minerals prepared in Example 1 and Example 2 were used to conduct adsorption and oxidation experiments on variable-valence heavy metal arsenic, and different experimental conditions were set to test its stability, and the economic benefits of synthesizing iron-containing layered silicate minerals and other minerals for removing arsenic were calculated and compared. The results are as follows Figure 5 , Figure 6 , Figure 7 , Figure 8 and Fig. 9 shown.

[0054] From the attached Figure 1 The specific surface area and cation exchange capacity of the iron-containing layered silicate mineral materials in Examples 1 and 2 show that the specific surface area and cation exchange capacity of the iron-containing layered silicate mineral prepared in Example 1 are 11.99 m 2 / g and 128.19 meq / 100g, which are close to the cation exchange capacity of natural montmorillonite minerals. The specific surface area and cation exchange capacity of the iron-containing layered silicate mineral prepared in Example 2 are 151.68 m 2 / g and 23.39 meq / 100g, which are higher than those of natural 1:1 type phyllosilicate minerals. Therefore, its larger specific surface area and cation exchange capacity can be beneficial to the removal of variable valence heavy metals.

[0055] From the attached Figure 2 The X-ray diffraction patterns of the iron-containing phyllosilicate minerals in Examples 1 and 2 show that these minerals have certain layered structural characteristics. d 001 The values ​​are 12.46 Å and 7.24 Å respectively. After the two iron-containing phyllosilicate minerals were treated with natural oriented flakes, ethylene glycol saturation and high temperature, it can be seen that the iron-containing phyllosilicate mineral prepared in Example 1 has a certain expansion property. d 001 The value is 13.39 Å; while the d 001 The value is 7.21 Å. After high-temperature calcination (calcination at 550°C for 2 hours), the diffraction peak (001) of the iron-containing layered silicate mineral prepared in Example 2 disappears.

[0056] The above results show that Example 1 is a 2:1 type phyllosilicate mineral with expansion, and Example 2 is a 1:1 type kaolinite-like phyllosilicate mineral. (Note: NDP is natural oriented flake treatment, EDG is ethylene glycol saturation treatment) From the attached Figure 3 It can be seen from the Fourier infrared spectra of the iron-containing layered silicate minerals in Example 1 and Example 2 that the spectrum lines show characteristic peaks of iron-containing layered silicate minerals, such as ~3433 cm -1 Hydroxyl stretching vibration peak of water, ~1636cm -1 Hydroxyl deformation vibration peak, ~1014 cm -1 Si-O-Si stretching vibration peak, ~455cm -1 The deformation vibration peak of Si-O-Si at 622 cm-1 The Fe-O deformation vibration peak at

[0057] This indicates that iron-containing layered silicate minerals were successfully synthesized.

[0058] From the attached Figure 4 The scanning electron microscope image of the iron-containing layered silicate mineral in Example 1 shows that the surface of the iron-containing layered silicate mineral is smooth, dense and thin, and presents a porous structure, which is conducive to the adsorption of variable-valence heavy metals. The surface of the iron-containing layered silicate mineral in Example 2 is rougher, without a complete thin-sheet structure, and looks relatively collapsed, but also presents a porous structure, which is also conducive to the adsorption of variable-valence heavy metals.

[0059] The effects of adsorption and oxidation of heavy metals by the iron-containing layered silicate minerals prepared in Example 1 (left) and Example 2 (right) were tested in a neutral water environment. Figure 5 As shown, both iron-containing phyllosilicate minerals have adsorption and oxidation effects on variable-valence heavy metals. Specifically, the removal effect of the iron-containing phyllosilicate mineral prepared in Example 1 is better than that of the iron-containing phyllosilicate mineral prepared in Example 2.

[0060] This is because the iron-containing layered silicate mineral prepared in Example 1 has a removal rate of up to 99.8% for variable-valence heavy metal arsenic, and an oxidation efficiency of 61%. These two indicators are significantly better than the mineral prepared in Example 2, whose removal rate and oxidation efficiency are 76.7% and 39%, respectively.

[0061] The effect diagram of adsorption and oxidation of heavy metals by the iron-containing layered silicate minerals prepared in Example 1 and Example 2 was tested in weakly acidic and weakly alkaline water environments. Figure 6 shown.

[0062] The results show that the iron-containing silicate mineral prepared in Example 1 exhibits excellent arsenic fixation ability in a weakly acidic medium, with an arsenic removal rate and oxidation rate of 99.8% and 62%, respectively, and is not significantly affected by the decrease in pH. Its performance far exceeds that of natural minerals (nontronite: 74%; montmorillonite: 50-70%; kaolinite: 47.8-77.2%) and iron oxides (hematite: 78%; and is easily affected by pH fluctuations, and Fe (III) dissolution in acidic conditions leads to inactivation). However, in a weakly alkaline environment, the arsenic removal performance of the material is significantly attenuated, with the removal rate and oxidation rate dropping to 83.2% and 55%, respectively, but still maintaining a high removal efficiency and oxidation efficiency. The iron-containing silicate mineral prepared in Example 2 exhibits a reverse pH response characteristic. The baseline value (removal rate 76.7%, oxidation rate 39%) under relatively neutral conditions in a weakly alkaline environment increases the arsenic removal rate and oxidation rate to 83.7% and 40%, reflecting flexible environmental adaptability.

[0063] According to the above, the iron-containing layered silicate mineral with a Fe / Si ratio of 1.0 prepared in Example 1 has the best removal effect on variable-valence heavy metal arsenic. 4 3- ) conditions to observe the arsenic removal effect.

[0064] like Figure 7 As shown. It can be seen that the arsenic removal rate and oxidation rate of the iron-containing layered silicate mineral prepared in Example 1 were 76.5% and 43.6% respectively under strong interference conditions, which were 23.3% and 17.4% lower than the baseline values ​​under neutral conditions (removal rate 99.8%, oxidation rate 61%). This phenomenon reveals that there is a significant competitive adsorption behavior between phosphorus and arsenic on the mineral surface. It is worth noting that despite the significant performance attenuation, the iron-containing layered silicate material still maintains more than 76% of the As fixation capacity. The high specific surface area and its layered structure provide sufficient adsorption sites, while the interlayer Fe-OH groups maintain partial oxidation activity through coordination.

[0065] The environmental stability of the Fe / Si=1.0 iron-containing phyllosilicate mineral (Example 1) to fixed arsenic was evaluated by TCLP (Toxicity Characteristic Leaching Procedure) test. Figure 8 As shown in the figure, after 18 hours of dynamic leaching, the total leached concentration of As in the material was 0.24 mg / L (extract #1) and 0.53 mg / L (extract #2), which was significantly lower than the threshold limit (5 mg / L) specified by the US Environmental Protection Agency (EPA). In addition, in extract #2, the leached As was mainly in the form of pentavalent arsenic. These indicate that the material not only has excellent arsenic fixation ability, but also maintains continuous oxidation activity.

[0066] Under the premise of homogeneity of equipment depreciation, energy consumption, and transportation and storage costs, the economic benefits of calculating and comparing the total cost of raw materials required for treating 1 ton of arsenic-containing wastewater (10 mg / L) with natural iron-containing phyllosilicate minerals and synthetic iron-containing phyllosilicate minerals are shown in Fig. 9 .

[0067] It can be seen that the synergy between raw material cost and processing efficiency dominates the economic differences.

[0068] The results show that Fe / Si=1.0 iron-containing layered silicate minerals show significant cost advantages, with a unit treatment cost of only 10.55 yuan / ton, which is 81.6% lower than that of natural similar materials (57.5 yuan / ton). This is attributed to the higher As removal rate (99.8%) of synthetic materials, and the arsenic concentration of the effluent can be reduced to 0.02 mg / L in a single treatment, meeting the GB 5749-2022 drinking water standard (<0.01 mg / L requires secondary treatment); the hydrothermal synthesis process maximizes the utilization of raw materials. By comparison, although the Fe / Si=1.5 synthetic material requires 5 cycles of treatment (total cost 50 yuan / ton) to meet the standard, its cost is still 13% lower than that of natural materials, which is attributed to the improvement of adsorption kinetics due to the increased density of Fe-O active sites on the material surface. It is worth noting that iron oxide materials present differentiated economic characteristics. Ferrihydrite achieves an ultra-low cost of 7.2 yuan / ton due to its high reactivity (removal rate of 99.9%), but its metastable characteristics lead to an environmental risk premium; the economic benefits of magnetite (16 yuan / ton) and hematite (26 yuan / ton) are lower than those of iron-containing silicate mineral materials with Fe / Si=1.5, but the stability advantage compared to iron-containing silicate minerals with Fe / Si=1.0 requires the cost of high dosage.

[0069] In summary, in scenarios where the risk of secondary pollution is strictly controlled (such as drinking water source remediation), Fe / Si=1.0 iron-containing layered silicate mineral materials should be given priority; in short-term emergency treatment, ferrihydrite can be used as an economical alternative.

[0070] The above embodiments are only preferred exemplary embodiments of the present application, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any person skilled in the art can easily think of development or replacement within the technical scope disclosed in the present invention, which are all within the protection scope and disclosure scope of the present invention.

Claims

1. An iron-based silicate material for efficiently removing variable-valence heavy metals, characterized in that: The invention is prepared from the following raw materials, wherein the raw materials include ferrous sulfate heptahydrate, sodium orthosilicate and sodium dithionite; wherein ferrous sulfate heptahydrate and sodium orthosilicate are used as iron sources and silicon sources, sodium dithionite is used as a reducing agent, the molar ratio of ferrous sulfate heptahydrate and sodium orthosilicate is 1:1-3:2, and the mass percentage of iron in the silicate mineral material is not less than 10%.

2. The iron-based silicate material for efficiently removing variable-valence heavy metals according to claim 1, characterized in that: The molar ratio of Fe / Si is 1.0-1.

5.

3. The iron-based silicate material for efficiently removing variable-valence heavy metals according to claim 1 or 2, characterized in that: The iron-containing layered silicate mineral material has a content of not less than 11.99m 2 / g specific surface area and a cation exchange capacity of not less than 23.39meq / 100g.

4. A method for preparing an iron-based silicate material for efficiently removing variable-valence heavy metals according to any one of claims 1 to 2, characterized in that: The steps include: S1: dissolving ferrous sulfate heptahydrate in deionized water, adding sodium dithionite and sodium orthosilicate under stirring, and continuously stirring to obtain a mixed suspension; S2: subjecting the mixed suspension obtained in step S1 to a hydrothermal reaction to obtain a reaction composition; S3: washing, centrifuging and freeze-drying the reaction product obtained in step S2 to obtain an iron-containing layered silicate mineral.

5. The method for preparing an iron-based silicate material for efficiently removing variable-valence heavy metals according to claim 4, characterized in that: The molar ratio of the ferrous sulfate heptahydrate to the sodium orthosilicate is 1:1-3:

2.

6. The method for preparing an iron-based silicate material for efficiently removing valence-varying heavy metals according to claim 4, characterized in that: The Fe / Si molar ratio is 0.5–2.

0.

7. The method for preparing an iron-based silicate material for efficiently removing valence-varying heavy metals according to claim 4, characterized in that: The hydrothermal reaction temperature in step S2 is 130-160° C., and the hydrothermal reaction time is 4-10 days, preferably 6-8 days.

8. The use of the iron-based silicate material for efficiently removing valence-modified heavy metals according to any one of claims 1 to 2, characterized in that: The steps include: S1: dispersing the iron-containing layered silicate mineral material in deionized water to prepare an iron-containing layered silicate mineral suspension, and adjusting the pH value of the suspension with a buffer solution; S2: using a buffer to adjust the pH value of the variable valence heavy metal solution to be the same as the pH value of the iron-containing layered silicate mineral suspension in S1; S3: Mixing the variable valence heavy metal solution and the iron-containing layered silicate mineral suspension.

9. The use of the iron-based silicate material for efficiently removing valence-modified heavy metals as claimed in claim 8, characterized in that: The buffers in S1 and S2 are MES and MOPS.

10. The use of the iron-based silicate material for efficiently removing valence-changing heavy metals as claimed in claim 8, characterized in that: The heavy metal is arsenic.

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